Get selected UI-Language in python
Both methods are provided by Blender API.
A way to list all installed localisation
&gt;&gt;&gt; bpy.app.translations.locales
('en_US', 'es', 'ja_JP', 'sk_SK', 'vi_VN', 'zh_CN', 'ar_EG', 'de_DE', 'fr_FR', 'it_IT', 'ko_KR', 'pt_BR', 'pt_PT', 'ru_RU', 'uk_UA', 'zh_TW', 'ab', 'ca_AD', 'cs_CZ', 'eo', 'eu_EU', 'fa_IR', 'ha', 'he_IL', 'hi_IN', 'hr_HR', 'hu_HU', 'id_ID', 'ky_KG', 'nl_NL', 'pl_PL', 'sr_RS', 'sr_RS@latin', 'sv_SE', 'th_TH', 'tr_TR')

A way to check for the chosen localisation
&gt;&gt;&gt; bpy.context.preferences.view.language
'de_DE'

&gt;&gt;&gt; bpy.context.preferences.view.use_translate_interface
True

&gt;&gt;&gt; bpy.context.preferences.view.use_translate_new_dataname
True

&gt;&gt;&gt; bpy.context.preferences.view.use_translate_tooltips
True